ITV is celebrating 50 years on our screens - and its influence has been instrumental in raising the standard of its rival, the BBC, its former director of programmes David Liddiment tells the BBC News website.

Bruce Forsyth rose to fame on Sunday Night at the London Palladium

When ITV launched on 22 September 1955, the BBC's television service had been running unchallenged for almost two decades and was fast gaining popularity.

But with no competition, it had become "inward-looking, pompous and elitist", former BBC and ITV grandee Greg Dyke recently wrote, while the BBC's official history admits it had become "dull and complacent".

While the corporation was able to rest on its public service principles, ITV was funded by advertising and so had to reach out to a mass audience.

Light entertainment hits like Sunday Night at the London Palladium, US imports Dragnet and I Love Lucy and quiz shows such as Take Your Pick soon became key planks in the ITV schedule.

And in just two years, ITV had won over 72% of the audience share from the BBC.

Tony Hancock appeared on both ITV and the BBC in the 1950s

After ITV secured enough fans and funding, it was also able to challenge the corporation's supremacy in public service genres with pioneering series such as Armchair Theatre and World in Action.

The effect on the BBC was "seismic", according to former ITV director of programmes David Liddiment, who says the corporation was "shocked into hitting back".

"The whole nature of the BBC began to change as they too recognised that they had to engage the whole community, the whole country, if the BBC was to remain sustainable," he says.

The BBC's response came in the form of more in-touch and up-to-date shows from Z Cars and Doctor Who to Top of the Pops and Match of the Day.

Coronation Street has been the mainstay of the ITV schedules

But from 1960, ITV had another weapon - while not the first soap, Coronation Street was on twice a week and is regarded as the first to truly represent the UK's working-class heartlands.

"I think that did prompt the BBC to think hard about both the range of its drama and the kind of drama that it did," says Mr Liddiment, who was executive producer of Coronation Street from 1987-92.

The BBC came up with several popular soaps in the 1960s, but ratings were still not the top priority and they were dropped after several years.

"When the landscape became more competitive in the late '70s and early '80s, there was no doubt at all that the BBC looked jealously on the power of Coronation Street to anchor the schedule," Mr Liddiment says.

"And EastEnders undoubtedly was an attempt, and a very successful attempt, for BBC One to have its own Coronation Street."

ITV was more prepared to ask the difficult question, it was more prepared to challenge the establishment view

David Liddiment

Drama was not the only area where ITV led the way. In news, ITN was less reverential than the BBC had traditionally been.

"ITV was more prepared to ask the difficult question, it was more prepared to challenge the establishment view," Mr Liddiment says.

"I think without ITV, the BBC would have continued to feel more like the state broadcaster - and in that respect, I think ITV did the BBC a great service."

ITN created the role of the newscaster as a TV personality and Granada was the first broadcaster to film an election, he adds.

World in Action was ITV's flagship current affairs show

In light entertainment, another regional ITV company, ATV, led the way with Sunday Night at the London Palladium, The Golden Shot and The Morecambe and Wise Show.

"There's no doubt at all that the advent of ATV as part of ITV stirred the competitive juices of BBC light entertainment," Mr Liddiment says.

"You started to see not just the ratings war but the contract war as each channel sought to sign up key talent."

Bruce Forsyth, Tony Hancock and Morecambe and Wise were among those in demand from both the BBC and ITV.

And while both broadcasters had their ups and downs, ITV continued to force the BBC to examine itself when it was outperformed.

Dramas like The Jewel in the Crown are some of ITV's highlights

In the early 1980s, ITV produced absorbing home-grown dramas like Brideshead Revisited and The Jewel in the Crown - but BBC One's backbone came from US shows like The Thorn Birds.

"There was an outcry that while the commercial channel was playing this extraordinarily rich and subtle-textured period drama, the BBC were playing in peak time a pretty cheap airport novelisation mini-series," Mr Liddiment says.

"It's moments like that where the governors of the BBC wake from their slumber and say 'this isn't quite what we had in mind'."

While many believe ITV is not currently on top form, the battle for ratings and relevance is more ruthless than ever - meaning channels must work even harder to keep viewers glued to their sets.